The fundamental aim of a television system is to extend the
sense of sight beyond its natural limits, along with the sound associated with
the scene being televised. Essentially then, a TV system is an extension of the
science of radio communication with the additional complexity that besides
sound the picture details are also to be transmitted.
In most television systems, as also in the C.C.I.R. 625
line monochrome system adopted by India, the picture signal is amplitude
modulated and sound signal frequency modulated before transmission. The carrier
frequencies are suitably spaced and the modulated output radiated through a
common antenna. Thus each broadcasting station can have its own carrier
frequency and the receiver can then be tuned to select any desired station.